There are various kinds of resin films as covering materials for agricultural houses and the like. Above all, films of fluororesins represented by ETFE (ethylene-tetrafluoroethylene copolymer) have been noted as materials good in transparency and excellent in weather resistance even to outdoor exposure over a period of 10 years or more.
Of films for agricultural use, for example, one used in a configuration of being fixed by aluminum holding members at intervals of 50 cm to 200 cm does not flutter in the wind or the like, so that the life of the film is evaluated from weather resistance to light or rain.
On the other hand, according to a configuration of usage, durability to friction or bending is required in some cases. For example, when the film is used in a configuration of being fixed at four sides of its periphery and being fixed by fixing bands commonly called mica wires between arch-shaped pipes, in a semi-cylindrical house or the like; or when the film is used as a lower layer film of a two-layer air house which has recently been noted as an energy-saving house, friction or pounding occurs at contact portions of the film with metal frames when the film flutters in the wind. The film is therefore liable to be broken by the repetition thereof. The pounding to the metal indicates a phenomenon that the film comes into contact with metal pipes and the like blown by wind without interruption, in the case where peripheral edges of the film are not fixed or the like.
When breakage thus occurs, good weather resistance which is a characteristic of the fluororesin film is not sufficiently utilized. Even when the film itself is not deteriorated, repairing or re-covering thereof becomes necessary to cause a problem of increased labor and cost.
Further, when the fluororesin film is subjected to outdoor exposure over a long period of 10 years or more, crystallization gradually proceeds to deteriorate repeated-bending characteristics. For example, when the film is used in a mode of a so-called “roll-up use” which is configured so that roll-up/roll-down are possible in order to ventilate the inside of a house, breaks (cracks) due to friction and repeated bending are liable to occur. Accordingly, a film which can withstand this use has been desired.
Although patent literature 1 relates to a fluorine-based resin used for resin coating and the like, not for an agricultural film, it is described therein that an inorganic filler or a pigment is incorporated in order to improve wear resistance and hue, and that the filler or the pigment is treated with a silane coupling agent, thereby improving dispersibility in the fluorine-based resin. Mica is described in the examples of the inorganic fillers and the pigments.
Patent literature 2 relates to an agricultural film formed of a material which is not a fluororesin, and there is described the agricultural film comprising a laminate comprising: a layer composed mainly of a low-density polyethylene resin; and two layers composed mainly of an ethylene-vinyl acetate copolymer and different from each other in vinyl acetate content, wherein mica is allowed to be contained in at least one layer thereof, thereby increasing both scattered-light transmittance and total-light transmittance. It is described that the mica is not particularly limited in its kind and may be natural mica or synthetic mica, and that mica generally used is employed.
In patent literature 3, there is described a method of dispersing composite particles into a resin, in which the composite particles has a constitution of amorphous silica-cerium oxide-base pigment from the outermost layer side, in order to improve light diffusibility and UV protection properties of the fluororesin film. Silica, talc and mica are exemplified as the base pigments. The composite particles used herein have an average particle size of 1 to 3 μm.
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